Light-sensitive materials comprising a light-sensitive layer containing silver halide, a reducing agent and a polymerizable compound provided on a support can be used in an image forming method in which a latent image of silver halide is formed, and then the polymerizable compound is polymerized to form the corresponding image.
Examples of said image forming methods are described in Japanese Patent Publication Nos. 45(1970)-11149 (corresponding to U.S. Pat. No. 3,697,275), 47(1972)-20741 (corresponding to U.S. Pat. No. 3,687,667) and 49(1974)-10697, and Japanese Patent Provisional Publication Nos. 57(1982)-138632, 57(1982)-142638, 57(1982)-176033, 57(1982)-211146 (corresponding to U.S. Pat. No. 4,557,997), 58(1983)-107529 (corresponding to U.S. Pat. No. 4,560,637), 58(1983)-121031 (corresponding to U.S. Pat. No. 4,547,450) and 58(1983)-169143. In these image forming methods, when the exposed silver halide is developed using a developing solution, the polymerizable compound is induced to polymerize in the presence of a reducing agent (which is oxidized) to form a polymer image. Thus, these methods need a wet development process employing a developing solution. Therefore, the process takes a relatively long time.
An improved image forming method employing a dry process is described in Japanese Patent Provisional Publication Nos. 61(1986)-69062 and 61(1986)-73145 (the contents of both publications are described in U.S. Pat. No. 4,629,676. In this image forming method, a recording material (i.e., light-sensitive material) comprising a light-sensitive layer containing a light-sensitive silver salt (i.e., silver halide), a reducing agent, a cross-linkable compound (i.e., polymerizable compound) and a binder provided on a support is imagewise exposed to form a latent image, and then the material is heated to polymerize within the area where the latent image of the silver halide has been formed. The above method employing the dry process and the light-sensitive material employable for such method are also described in Japanese Patent Provisional Publication Nos. 61(1986)-183640, 61(1986)-188535 and 61(1986)-228441.
The above-mentioned image forming methods are based on the principle in which the polymerizable compound is polymerized in the portion where a latent image of the silver halide has been formed.
Further, Japanese Patent Provisional Publication No. 61(1986)-260241 describes another image forming method in which the polymerizable compound in a portion where a latent image of the silver halide has not been formed is polymerized. In the method, when the material is heated, the reducing agent functions as polymerization inhibitor in the portion where a latent image of the silver halide has been formed, and the polymerizable compound in the other portion is polymerized.
Japanese Patent Provisional Publication Nos. 61(1986)-275742 and 61(1986)-278849 describe an embodiment of the light-sensitive material, which employs microcapsules containing at least two components of the light-sensitive layer, that is polymerizable compound and a color image forming substance. The light-sensitive material having such a structure has an advantage of giving an image of high quality.
The light-sensitive material which contains a silver halide grain as a photosensor generally causes occurrence of fog in the unexposed area. The occurrence of the fog depends on characteristics of silver halide, or variation of the processing conditions such as heating temperature and humidity. Since the above image-forming method is performed using a heat development process at a high temperature, the occurrence of fog increases. Therefore, the contrast in the obtained image lowers.
Various methods have been heretofore proposed to keep the obtained image from fogging. A method in which the known compound as an anti-fogging agent is introduced at a stage of preparation of a silver halide emulsion is described in the above publications. It is known that silver halide grains having various grain forms (i.e., crystal structure) can be obtained by selecting the method for preparation and/or the silver halide composition. A silver halide grain reduced in the occurrence of fog can be obtained.
Various silver halide grains can be used to match with the desired light-sensitive material. A silver halide grain having a core/shell structure is employed in order to give an image which has a high sensitivity. However, when the silver halide grain having a core/shell structure is employed, the occurrence of fog is apt to increase. Accordingly, the quality of the image lowers.
The light-sensitive material comprising a light-sensitive layer containing a silver halide grain having a core/shell structure, and the silver iodide content in the shell is higher than that in the core has been filed by the present applicant (U.S. Ser. No. 012,462).